Field of the Invention
This disclosure relates to a sheet discharge apparatus, a sheet processing apparatus, and an image forming apparatus.
Description of the Related Art
In general, there is known an image forming apparatus which discharges a sheet, on which an image is formed, by a sheet discharge apparatus and stacks the sheet on a discharge tray. In addition, a sheet processing apparatus may be provided in the image forming apparatus to perform a binding process on the sheet where the image is formed. In this case, the sheet on which the image is formed is conveyed to the sheet processing apparatus to be subjected to the binding process, and then a sheet bundle is discharged by the sheet discharge apparatus and stacked on the tray.
Hitherto, JP-A-2009-113958 discloses such a sheet discharge apparatus in which, when the sheet bundle subjected to the binding process is discharged, a sheet discharge speed is accelerated in order that a binding portion of the discharged sheet bundle does not interfere with the binding portion of the already-stacked sheet bundle.
By the way, when a predetermined amount of sheets are stacked on the tray stacked with the discharged sheet or the sheet bundle (even in a case where sheets are bound in a sheet bundle and discharged, there is no difference in that the sheet is discharged, and thus in the following it is assumed that the sheet bundle is also included in the meaning of the sheet if there is no specific mention about the sheet bundle or the sheet separated one by one), the tray descends to enable the next sheet to be stacked. Then, after the tray descends, the next sheet is discharged and sequentially the sheet is stacked on the tray. However, the sheets to be stacked on the tray is limited in amount, and thus when the stacking amount of the sheets stacked on the tray is in a full loaded state up to the limit of the tray, the sheet processing apparatus and the image forming apparatus are stopped. In this case, when the sheet is removed by a user, the tray is raised. When the raised tray is returned to a home position, the sheet processing apparatus and the image forming apparatus are reactivated, and the sheet is discharged onto the tray.
In order to prevent that the sheet processing apparatus and the image forming apparatus are stopped at the time of the full loaded state, or in order to temporally check the stacked sheet, the user may remove the stacked sheet during operation. Even in a case where the stacked sheet is removed during operation as described above, the sheet discharge apparatus disclosed in JP-A-2009-113958 already described above keeps on discharging the next sheet bundle at the increased sheet discharge speed in order that the binding portion of the discharged sheet bundle interferes with the binding portion of the stacked sheet bundle.
Herein, in a case where the stacked sheet is removed, the height position of the uppermost surface of the sheet on the tray is lowered. In this state, when the sheet is discharged, the leading end of the discharged sheet is hung down a lot. When the hanging-down amount of the leading end of the sheet is large, an abutting angle formed between the leading end and the uppermost surface of the sheet becomes large compared to that before the stacked sheet is removed. It is noted that, in a case where all the stacked sheets are removed, the abutting angle formed between the leading end of the sheet and the sheet stack surface of the tray becomes large.
Then, when the abutting angle becomes large, a discharge resistance between the leading end of the sheet and the sheet on the tray becomes large. When the discharge resistance becomes large, strength (stiffness) of the sheet becomes small compared to the resistance, and thus the sheet is buckled. As a result, the trailing end of the sheet leans onto a sheet discharge unit, and a paper jam occurs.